Synthesis Of Cu-based Layered Materials And Their Catalytic Oxidation Properties

Fenton oxidation is an environmentally friendly technology and efficiently utilized in wastewater treatment process for the degradation of organics.Fenton reaction encompass the reaction of Fe2+and H2O2 to form hydroxyl radicals(HO·)with strong oxidizing ability that can oxidize organic compounds.Homogeneous Fenton process is strongly dependent on the solution pH,the dosage of Fe2+and H2O2.Meanwhile,ferric hydroxide precipitate is formed after reaction,which can cause secondary pollution.Heterogeneous Fenton catalyst can be easy to separate with wastewater and prevent the formation of iron sludge.Copper(Cu)exhibits great Fenton catalytic activity,can promote the genernation of HO·from H2O2 and degrade organics into CO2/H2O or other non-toxic small molecule hydrocarbons.However,most Cu catalysts including mixed metal oxides and supported metal oxides whose active sites are easily aggregation and difficult to achieve highly dispersion.Layered double hydroxides(LDHs),have advantages of high and uniform metal dispersion and the flexibility in composition,it shows potential and promising application in catalysis field.Thus,a series of Cu LDHs with various divalent metals(Ni and Co)and tetravalent metals(Ti and Sn)were prepared by co-precipition method and used as Fenton catalyst for phenol degradation.The results are listed as follows.1.A series of Cu LDHs containing Ni and Co were synthesized.Copper hydroxide(Cu(OH)2)was observed with the increased Cu/Ni molar ratio.2.LDHs are composed of edge-sharing MO6 octahedra,in which each metal cation is connected by metal-oxygen-metal bridge linkages(M1-O-M2).Such linkages and MO6 octahedra could facilitate the synergistic effect among metals,promoting the genernation of active center Cu+.The most active catalyst Cu0.5Ni2.5Fe LDHs can mineralize all phenol in feed at ambient pH and less excessive H2O2 dosage.3.A possible mechanism based on the electron transfer among metals in CuNiFe LDHs and the HO· generation is proposed.The metal-oxo-metal bridges and highly dispersed MO6 octahedra in LDHs allow the electron transfer from Ni2+to Cu2+,producing Ni3+and Cu+.Cu+species could be primary active sites to react with H2O2 to generate HO· and Cu2+.As a result,phenol can be degraded to CO2 and H2O.Cu+could be regenerated by the electron transfer from Cu2+to Ni2+in LDHs.Fe3+in the brucite-like sheets may also make contributions to phenol degradation via Fenton-like reaction.The recovery of Fe3+ could be achieved by H2O2.The percentage of Cu+and the phenol degradation rate increase with the decreased Cu/Ni ratio.4.Titanium(Ti)and Tin(Sn)were introduced into LDHs to bulid the new ternary metal system and used for phenol degradation.Cu1Ni2Sn0.75 LDHs can mineralize 97%phenol in feed at ambient pH and H2O2 dosage of 0.6 mL.5.A possible mechanism of phenol degradation via CuNiSn LDHs is proposed.Metal-oxo-metal bridges in LDHs can allow the effective electron transfer from Ni2+ to Cu2+to generate Cu+;Sn4+could help with the formation of Ni2+ and Cu2+;Sn4+could be regenerated by the electron transfer from Sn2+to Ni3+in LDHs.All the metals with different valences can be regenerated in this system.